Technical Field
The invention relates to solid freeform fabrication technology, and particularly to photo-sodification modeling technology for forming a three-dimensional object from a light-curable material.
Related Art
Photo-sodification modeling technology produces a three-dimensional object by stacking and bonding thin layers of solid-state formed from a light-curable liquid resin. There are two conventional approaches for the implementation of the conventional photo-sodification modeling devices, i.e., the stereolithography machines.
The first approach is to make the light patterns projected from the top to the tank to cure the liquid light curing material in the tank. For this top-down configuration, the size of the tank must be able to maintain adequate resin in which an object to be printed is completely immersed. The surface of the resin needs to be leveled before the exposure of each layer, thereby ensuring uniformity of each layer. In addition, the surface of the resin in the process of printing does not stay at the same level, and the vertical displacement then needs to be compensated in order to maintain the same thickness of each layer to be printed. Further, the photo-solidification occurs on the surface of the light-curable resin in contact with air. For this reason, the problem of oxygen inhibition increased the curing time of the resin.
The second approach is to make light patterns projected from a place under the tank to the transparent bottom of the tank so as to cure the liquid light-curable material. This approach can improve the drawback of the above stereolithography machine, for example, to simplify the structure of the machine and result in a significant reduction in the volume of the tank. In addition, a cured layer is formed between the bottom of the tank and a previous cured layer or a formation platform. Since the cured layer is not formed over the surface of the liquid light-curable material in contact of the air, the problems of uniformity of layers and oxygen inhibition will cease to exist, and it no longer needs a resin surface leveling device in the machine. Each layer is separated from the bottom of the tank, and is elevated to reserve space for the next layer to be printed.
However, since the result of the Van der Waals force, chemical bonding force and attractive force, an adhesion phenomenon occurs between the cured layer and the tank, resulting in difficulties in pulling the cured layer by the formation platform. The magnitude of the separation force is directly correlated with the strength of the above forces and the area of the cured layer, and is one of the most important limiting factors to the printing of high resolution. In order to reduce adhesion, some technology for improvement of sticking phenomenon employs an elastic membrane, such as Teflon or silicone at the bottom of the tank, thereby to prevent the cured layer from sticking to the tank. However, the separation force is still too large to print finely, even with these improvements.